Re: [PATCH 1/7] signal.h: Define SIGINFO on all architectures

From: Eric W. Biederman
Date: Tue Jun 11 2019 - 16:40:58 EST

Arseny Maslennikov <ar@xxxxxxxxx> writes:

> This complementary patch defines SIGINFO as a synonym for SIGPWR
> on every architecture supported by the kernel.
> The particular signal number chosen does not really matter and is only
> required for the related tty functionality to work properly,
> so if it does not suite expectations, any suggestions are warmly
> welcome.
>
> SIGPWR looks like a nice candidate for this role, because it is
> defined on every supported arch; it is currently only used to inform
> PID 1 of power failures, and daemons that care about low-level
> events do not tend to have a controlling terminal.
>
> However, on sparcs SIGPWR is a synonym for SIGLOST, a signal unique
> to that architecture, with a narrow set of intended uses that do not
> combine well with interactively requesting status.
> SIGLOST is not used by any kernel code at the moment.
> I'm not sure there is a more reasonable alternative right now.

Is the name SIGINFO already well established.

It just is a little bit confusing with struct siginfo.

At least on x86 it looks like we have signals 32 and 33 that are
reserved and not used for anything. Is there a reason you have
not picked one of those?

Also should this be a realtime signal with signal information
or a non-realtime signal?

I don't expect there is much to encode except that the user is asking
for information. I half wonder if it could be done as a different
si_code to SIGWINCH. But of course that doesn't work because it is
not a real time signal so does not queue more than one siginfo. (Sigh).

I just would like to see that we have a clear concept of how this new
signal plays into all of the signal handling bits.

Added linux-api because this is fundamentally extending the linux-api,
and we probably want man-page updates etc.

Eric

>
> Signed-off-by: Arseny Maslennikov <ar@xxxxxxxxx>
> ---
> arch/arm/include/uapi/asm/signal.h | 1 +
> arch/h8300/include/uapi/asm/signal.h | 1 +
> arch/ia64/include/uapi/asm/signal.h | 1 +
> arch/m68k/include/uapi/asm/signal.h | 1 +
> arch/mips/include/uapi/asm/signal.h | 1 +
> arch/parisc/include/uapi/asm/signal.h | 1 +
> arch/powerpc/include/uapi/asm/signal.h | 1 +
> arch/s390/include/uapi/asm/signal.h | 1 +
> arch/sparc/include/uapi/asm/signal.h | 2 ++
> arch/x86/include/uapi/asm/signal.h | 1 +
> arch/xtensa/include/uapi/asm/signal.h | 1 +
> include/uapi/asm-generic/signal.h | 1 +
> 12 files changed, 13 insertions(+)
>
> diff --git a/arch/arm/include/uapi/asm/signal.h b/arch/arm/include/uapi/asm/signal.h
> index 9b4185ba4f8a..b80b53a17267 100644
> --- a/arch/arm/include/uapi/asm/signal.h
> +++ b/arch/arm/include/uapi/asm/signal.h
> @@ -50,6 +50,7 @@ typedef unsigned long sigset_t;
> #define SIGLOST 29
> */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> #define SIGUNUSED 31
>
> diff --git a/arch/h8300/include/uapi/asm/signal.h b/arch/h8300/include/uapi/asm/signal.h
> index e15521037348..7a2b783af22b 100644
> --- a/arch/h8300/include/uapi/asm/signal.h
> +++ b/arch/h8300/include/uapi/asm/signal.h
> @@ -50,6 +50,7 @@ typedef unsigned long sigset_t;
> #define SIGLOST 29
> */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> #define SIGUNUSED 31
>
> diff --git a/arch/ia64/include/uapi/asm/signal.h b/arch/ia64/include/uapi/asm/signal.h
> index aa98ff1b9e22..b4c98cb17165 100644
> --- a/arch/ia64/include/uapi/asm/signal.h
> +++ b/arch/ia64/include/uapi/asm/signal.h
> @@ -45,6 +45,7 @@
> #define SIGLOST 29
> */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> /* signal 31 is no longer "unused", but the SIGUNUSED macro remains for backwards compatibility */
> #define SIGUNUSED 31
> diff --git a/arch/m68k/include/uapi/asm/signal.h b/arch/m68k/include/uapi/asm/signal.h
> index 915cc755a184..a0b4e4108cb8 100644
> --- a/arch/m68k/include/uapi/asm/signal.h
> +++ b/arch/m68k/include/uapi/asm/signal.h
> @@ -50,6 +50,7 @@ typedef unsigned long sigset_t;
> #define SIGLOST 29
> */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> #define SIGUNUSED 31
>
> diff --git a/arch/mips/include/uapi/asm/signal.h b/arch/mips/include/uapi/asm/signal.h
> index 53104b10aae2..975a6f0d3b0b 100644
> --- a/arch/mips/include/uapi/asm/signal.h
> +++ b/arch/mips/include/uapi/asm/signal.h
> @@ -43,6 +43,7 @@ typedef unsigned long old_sigset_t; /* at least 32 bits */
> #define SIGCHLD 18 /* Child status has changed (POSIX). */
> #define SIGCLD SIGCHLD /* Same as SIGCHLD (System V). */
> #define SIGPWR 19 /* Power failure restart (System V). */
> +#define SIGINFO SIGPWR /* Keyboard status request (4.2 BSD). */
> #define SIGWINCH 20 /* Window size change (4.3 BSD, Sun). */
> #define SIGURG 21 /* Urgent condition on socket (4.2 BSD). */
> #define SIGIO 22 /* I/O now possible (4.2 BSD). */
> diff --git a/arch/parisc/include/uapi/asm/signal.h b/arch/parisc/include/uapi/asm/signal.h
> index d38563a394f2..fe2e00d590ac 100644
> --- a/arch/parisc/include/uapi/asm/signal.h
> +++ b/arch/parisc/include/uapi/asm/signal.h
> @@ -22,6 +22,7 @@
> #define SIGUSR2 17
> #define SIGCHLD 18
> #define SIGPWR 19
> +#define SIGINFO SIGPWR
> #define SIGVTALRM 20
> #define SIGPROF 21
> #define SIGIO 22
> diff --git a/arch/powerpc/include/uapi/asm/signal.h b/arch/powerpc/include/uapi/asm/signal.h
> index 85b0a7aa43e7..e7f3885905b4 100644
> --- a/arch/powerpc/include/uapi/asm/signal.h
> +++ b/arch/powerpc/include/uapi/asm/signal.h
> @@ -53,6 +53,7 @@ typedef struct {
> #define SIGLOST 29
> */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> #define SIGUNUSED 31
>
> diff --git a/arch/s390/include/uapi/asm/signal.h b/arch/s390/include/uapi/asm/signal.h
> index 9a14a611ed82..12ee62987971 100644
> --- a/arch/s390/include/uapi/asm/signal.h
> +++ b/arch/s390/include/uapi/asm/signal.h
> @@ -58,6 +58,7 @@ typedef unsigned long sigset_t;
> #define SIGLOST 29
> */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> #define SIGUNUSED 31
>
> diff --git a/arch/sparc/include/uapi/asm/signal.h b/arch/sparc/include/uapi/asm/signal.h
> index ff9505923b9a..b655163198bb 100644
> --- a/arch/sparc/include/uapi/asm/signal.h
> +++ b/arch/sparc/include/uapi/asm/signal.h
> @@ -71,6 +71,8 @@
> #define SIGWINCH 28
> #define SIGLOST 29
> #define SIGPWR SIGLOST
> +/* XXX: is it OK for SIGINFO to collide with LOST? */
> +#define SIGINFO SIGPWR
> #define SIGUSR1 30
> #define SIGUSR2 31
>
> diff --git a/arch/x86/include/uapi/asm/signal.h b/arch/x86/include/uapi/asm/signal.h
> index e5745d593dc7..1539bb28826c 100644
> --- a/arch/x86/include/uapi/asm/signal.h
> +++ b/arch/x86/include/uapi/asm/signal.h
> @@ -55,6 +55,7 @@ typedef unsigned long sigset_t;
> #define SIGLOST 29
> */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> #define SIGUNUSED 31
>
> diff --git a/arch/xtensa/include/uapi/asm/signal.h b/arch/xtensa/include/uapi/asm/signal.h
> index 005dec5bfde4..d644234305de 100644
> --- a/arch/xtensa/include/uapi/asm/signal.h
> +++ b/arch/xtensa/include/uapi/asm/signal.h
> @@ -65,6 +65,7 @@ typedef struct {
> #define SIGPOLL SIGIO
> /* #define SIGLOST 29 */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> #define SIGUNUSED 31
>
> diff --git a/include/uapi/asm-generic/signal.h b/include/uapi/asm-generic/signal.h
> index 5c716a952cbe..9f9a1db0d43c 100644
> --- a/include/uapi/asm-generic/signal.h
> +++ b/include/uapi/asm-generic/signal.h
> @@ -43,6 +43,7 @@
> #define SIGLOST 29
> */
> #define SIGPWR 30
> +#define SIGINFO SIGPWR
> #define SIGSYS 31
> #define SIGUNUSED 31